Generally, a silver halide emulsion is prepared through the process of formation of silver halide grains by double decomposition of a soluble silver salt with a soluble halide in a aqueous gelatin solution, and then conducting a physical ripening process, a desalting process, and a chemical ripening process of the resulting emulsion.
A spectral sensitizing dye is, in general, added to a photographic emulsion already chemically sensitized before it is applied to a support. In U.S. Pat. No. 4,425,426 and the like, however, a method for adding a spectral sensitizing dye to a photographic emulsion before the beginning of or during the course of its chemical sensitization was disclosed. Further, in U.S. Pat. Nos. 2,735,766, 3,628,960, 4,183,756, and 4,225,666, methods for adding a spectral sensitizing dye to a photographic emulsion before completion of formation of silver halide grains were disclosed.
More particularly, in U.S. Pat. Nos. 4,183,756 and 4,225,666, it was disclosed that a method for adding a spectral sensitizing dye to a photographic emulsion after formation of stable nuclei during the formation process of silver halide grains had advantages such as an increase in photographic sensitivity and strengthened adsorption of the spectral sensitizing dye by silver halide grains.
In techniques disclosed so far relating to the spectral sensitization of photographic emulsions, the chemical ripening was always carried out in the presence of a spectral sensitizing dye. In such cases, however, the presence of spectral sensitizing dye likely reduces the photographic sensitivity of the emulsion.